This invention relates to heat exchangers and has particular but not necessarily exclusive reference to plate fin heat exchangers and has particular reference to heat exchangers intended for condensing at least part of a vapour to form a liquid.
Heat exchangers are often used in circumstances where a cooling stream of vapour forms a liquid condensate which condenses onto surfaces containing or within the cooling stream. Although a great deal of effort has been expended on research and development into boiling surfaces for heat exchangers--where a liquid phase is being converted into a vapour phase--less effort has been directed heretofor towards condensing surfaces. To date, the principal mechanism for improving the effectiveness of condensing surfaces has been to provide channels or ridges in the condensing surface which lead the condensed liquid to discrete parts of the surface, leaving the remainder clear of liquid and therefore able to operate more efficiently. Such surfaces are commonly referred to as "Grigorig" surfaces. The theory behind such Grigorig surfaces is that the major resistance to heat transfer is that of the liquid film which forms as a result of condensation. By leading the liquid film to certain areas, the remaining portions of surface are free of thick liquid films and therefore are able to transfer heat more readily from the vapour to the surface.
The present invention is concerned with heat exchangers in which there are provided fins within the condensing path. The principle application of heat exchangers incorporating fins is in the so-called plate fin heat exchangers.
In a plate fin heat exchanger, there is provided a series of vertically disposed, spaced, parallel plates which form a series of discrete flow paths--the flow paths being further defined by side members. Between the plates, there are disposed a series of fins, normally corrugated fins, and the assembly may be clamped together or is preferably bonded together. Frequently, plate fin heat exchangers are made from aluminium or aluminium alloys and may be joined together by means of salt bath brazing or vacuum brazing. Plate fin heat exchanger constructions are well known per se.